Inverter device and air conditioning system using inverter device

ABSTRACT

A current sensor for detecting a power supply current is commonly used for detecting a current of a stator winding to detect a rotational position of a magnet rotor, so that a sinusoidal driving is realized without adding two current sensors for detection of a phase current, and also a phase shift circuit and a comparator needed in the conventional 120-degree current feeding are not required, and the number of components can be reduced. Therefore, an inverter device with a low noise and low vibration, having a small size, light weight and high reliability is obtained.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an inverter device for driving andcontrolling a sensorless DC brushless motor, and to an air conditionerapplying such an inverter device to a motor-driven compressor using asensorless DC brushless motor as a driving source.

2. Description of the Related Art

The following explains an example of an air conditioner for a vehicle,which mounts a conventional motor-driven compressor using a sensorlessDC brushless motor as a driving source, and which includes a battery orother DC power source.

FIG. 20 shows a system configuration of an air conditioner for avehicle. In the drawing, reference numeral 101 is an air duct, and airis sucked in through an air inlet port 103 by an action of an indoor fan102, and after heat exchange by an indoor heat exchanger 104, the air isblown out into a vehicle compartment from an air blowout port 105.

A refrigeration cycle is constructed by the indoor heat exchanger 104together with a motor-driven compressor 106 using a sensorless DCbrushless motor as a driving source, a four-way changeover valve 107 forchanging flow of a refrigerant to select cooling or heating, a throttledevice 108, and an outdoor heat exchanger 110 for exchanging heat withfresh air by an action of an outdoor fan 109 (motor).

Reference numeral 111 is an inverter device for operating a sensorlessDC brushless motor as a driving source of the motor-driven compressor106, and the operation thereof together with the indoor fan 102,four-way changeover valve 107 and outdoor fan 109, is controlled by anair conditioner controller 112.

The air conditioner controller 112 is connected with an indoor fanswitch 113 for turning on or off the indoor blast and controlling thefan power, an air conditioner switch 114 for selecting cooling orheating, or turning off, a temperature control switch 115, and acommunication device 116 for communicating with a vehicle controller.

In this system, for example, when the blast is turned on and low poweris set by the indoor fan switch 113 and cooling is instructed by the airconditioner switch 114, the air conditioner controller 112 sets thefour-way changeover valve 107 as shown by a solid line in the diagram,and the indoor heat exchanger 104 is used as evaporator and the outdoorheat exchanger 110 as condenser, and the outdoor fan 109 is turned onand the indoor fan 102 is set to be a low power.

According to the temperature control switch 115, by varying a rotatingspeed of the motor-driven compressor 106 using the inverter device 111,the temperature of the indoor heat exchanger 104 is adjusted. Whencooling or heating is turned off by the air conditioner switch 114, themotor-driven compressor 106 and outdoor fan 109 are turned off.

When the indoor fan switch 113 is turned off, the indoor fan 102 isturned off, and the motor-driven compressor 106 and outdoor fan 109 arealso turned off in order to protect the refrigeration cycle.

On the other hand, when an OFF command of cooling or heating operationis received from a vehicle controller (not shown) via the communicationdevice 116 because of a reason of saving a power or protecting abattery, the air conditioner controller 112 conducts an action similarto turning off the cooling or heating operation conducted by the airconditioner switch 114.

FIG. 21 shows a motor-driven compressor having a sensorless DC brushlessmotor as an example of the conventional motor-driven compressor 106.

In the diagram, a compression mechanism 28, a motor 31 and others areinstalled in a metal casing 32.

The refrigerant is sucked in through a suction port 33, and when thecompression mechanism 28 (scroll mechanism, in this example) is drivenby the motor 31, the refrigerant is compressed. The compressedrefrigerant passes through the motor 31 in the metal casing 32 and thencools the motor 31, and is then discharged from a discharge port 34. Aterminal 39 connected to a winding of the motor 31 inside is connectedto the inverter device 111 in FIG. 20.

In an air conditioner for a vehicle mounting such a motor-drivencompressor, it is important to drive at a low noise and low vibrationfrom the viewpoint of riding comfort and effects of vibration on otherdevices. Especially in an electric car, since there is no engine, theoperation is very silent (in a hybrid electric car while running by amotor without starting engine), and further while stopping, themotor-driven compressor can be driven by a battery power source, and inthis case since there is no running noise or vibration, the noise andvibration of the motor-driven compressor will be more noticeable.

However, a current feeding system by the inverter device 111 adapted tothe conventional motor-driven compressor 106 is an 120-degree powerfeeding system, and a magnetic field change is an interval of 60 degrees(a current feeding in an interval of 60 degrees). For example, seePatent Document 1: Japanese Patent Laid-open Publication No. H8-163891,page 8, FIG. 4.

Accordingly, torque fluctuations are significant in the motor 31 fordriving the compression mechanism 28, and it was difficult to lower thenoise and vibration.

FIG. 22 shows a circuit example of a construction having the inverterdevice 111 and coupled with the motor portion of the motor-drivencompressor. In the diagram, reference numeral 121 is a battery, 122 isinverter operation switching elements connected to the battery 121, and123 are inverter operation diodes. Reference numeral 124 shows statorwindings of the motor, and 125 shows a magnet rotor of the motor.Reference numeral 126 is a current sensor which detects a power supplycurrent, calculates the power consumption, and protects the switchingelements. Reference numeral 127 is a phase shift circuit for detecting aposition of the magnet rotor 125 from a voltage of the stator windings124, and 128 is a comparator. Reference numeral 129 is a control circuitfor controlling the switching elements 122 on the basis of signals fromthe current sensor 126, comparator 128 and others.

On the other hand, in the case of a sinusoidal driving, since apermanent magnet rotor is driven by a continuous rotating magneticfield, torque fluctuations are small. Therefore, it is desired to use asinusoidal driving inverter device which produces sinusoidal current.For detection of a position of the permanent magnet rotor, two currentsensors are used for detecting the current of the stator windings. Forexample, see Patent Document 2: Japanese Patent Laid-open PublicationNo. 2000-333465, page 9, FIG. 2.

FIG. 23 shows another circuit example using the inverter device 111. Ascompared with the construction in FIG. 22, the comparator 128 and phaseshift circuit 127 are not provided, but there are further provided acurrent sensor 130 for detection of U-phase current and a current sensor131 for detection of W-phase current in order to detect the position ofthe magnet rotor 125 from the current of the stator windings. Thecontrol circuit 129 calculates the current of the other phase from thecurrent values of two phases from the two current sensors (two currentsensors are needed, but any two phases of the phases U, V, W will do),detects the position of the magnet rotor 125, and controls the switchingelements on the basis of the signals from the current sensor 126 andothers.

The current sensor 130 for detection of U-phase current and currentsensor 131 for detection of W-phase current are provided on the inverteroutput lines of which the potentials are always changing due to on/offapplication of a voltage of the battery 121, and therefore a photocoupler or the like is needed for signal transmission to the controlcircuit 129. As a result, the current sensors are complicated instructure, and a simple structure only by a shunt resistance can not berealized.

Aside from the low noise and low vibration, the air conditioner for avehicle is also demanded to be small in size and light in weight fromthe viewpoint of accommodation and running performance.

DISCLOSURE OF THE INVENTION

As described above, by using the sinusoidal driving inverter whichproduces a sinusoidal current, there is an advantage that torquefluctuations are smaller, but in the conventional structure shown inFIG. 23, two current sensors are needed for detecting the position ofthe magnet rotor, which becomes a hamper factor in achieving a smallersize and lighter weight of an air conditioner for a vehicle.

Such a demand for a smaller size and lighter weight is not limited to avehicle use, but is similarly applicable to such as a room airconditioner, and the smaller size and lighter weight are demanded inrelation to a downsizing design of equipments.

The invention is devised to solve the problems of the prior art, and itis hence an object thereof to provide an inverter device of a low noiseand low vibration, and small size and light weight.

The invention has another object to provide an air conditioner having amotor-driven compressor integrally mounting an inverter device of a lownoise and low vibration, having a small size and light weight.

To solve the problems, in the invention, a current sensor for detectinga power supply current is commonly used for detection of a current of astator winding so as to detect a rotational position of a magnet rotor.

That is, the inverter device according to a first aspect of theinvention is an inverter device for driving a sensorless DC brushlessmotor, which comprises an inverter circuit for switching adirect-current voltage obtained from a direct-current power source andsupplying an alternating-current current of a sinusoidal wave to thesensorless DC brushless motor; and current detecting means for detectinga power supply current between the direct-current power source and theinverter circuit. The sensorless DC brushless motor includes statorwindings of a three-phase wiring electrically connected to the invertercircuit and a magnet rotor, and the current detecting means is a singlecurrent detecting means which is used for commonly detecting the currentflowing in the stator windings, and by detecting the current flowing inthe stator windings as well as detecting the power supply current, arotational position of the magnet rotor is judged to thereby control theswitching of the inverter circuit.

In the inverter device, preferably, the direct-current voltage of thedirect-current power source may be switched by three-phase modulation.

Preferably, within a carrier period of the three-phase modulation, acurrent feeding time may be equally added or subtracted in a currentfeeding period in each phase of the stator windings.

In the inverter device, preferably, within a carrier period, a currentfeeding timing to each phase of the stator windings is shifted, so thatthe current flowing in the stator windings may be detected by thecurrent detecting means.

The inverter device of the invention may be also adapted to be mountedon a vehicle.

Further, the inverter device of the invention may be also adapted fordriving the sensorless DC brushless motor if the sensorless DC brushlessmotor is a driving source of the compressor.

According to the invention, a sinusoidal driving is possible withoutadding two current sensors for detection of a phase current, and a phaseshift circuit and a comparator needed in the conventional 120-degreecurrent feeding are not required, and hence the number of components isreduced, so that the inverter device achieving a low noise, lowvibration, having a small size, light weight, and high reliability isobtained.

The noise and vibration can be further lowered by switching thedirect-current voltage from the direct-current power source by thethree-phase modulation.

Further, by shifting the current feeding timing to each phase of thestator windings of the sensorless DC brushless motor within a carrierperiod, the rotational position can be detected in each carrier, and theoutput to the stator windings can be adjusted, so that the inverterdevice achieving small torque fluctuations, low noise, and low vibrationcan be obtained.

An air conditioner according to a second aspect of the invention ischaracterized by mounting the inverter device of the first aspect.

The air conditioner may preferably comprise the inverter deviceintegrally coupled to the compressor together with the sensorless DCbrushless motor.

In the integral structure with the compressor, the air conditioner maypreferably include a suction pipe, which is adapted to the compressor,for sucking a refrigerant for cooling the inverter device.

The inverter device may be disposed beneath the suction pipe or betweenthe suction pipe and the compressor.

According to the second aspect of the invention, by integrally formingas one body with the compressor, the inverter device including theinverter circuit can be cooled, and the reliability of the inverterdevice is assured.

A shunt resistor can be used as a current sensor, and a sinusoidaldriving is possible without adding two current sensors for detection ofa phase current, and the phase shift circuit and comparator needed inthe conventional 120-degree current feeding are not required, and hencethe number of components is reduced, so that there is an effect that theinverter device achieving a low noise, low vibration, having a smallsize, light weight, and high reliability is obtained.

Since the compressor can be driven at a low noise and low vibration, andvibration resistance reliability is high with a small size and lightweight, and hence, for example, the inverter device is appropriate forvehicle use.

By switching by three-phase modulation, the noise and vibration can befurther lowered.

By the arrangement of shifting the current feeding in the carrier, asituation of detecting only one phase is eliminated (decreased), and theposition detection may be further enhanced to be an effect.

In the three-phase modulation, all three phases of the stator windingscan be detected, and a current calculation of the remaining phase afterdetection of two phases is not needed.

In the three-phase modulation according to the invention, the currentfeeding in the carrier is configured to be added or subtracted in allthree phases, and a situation of detecting only one phase is eliminated,and the position detection may be further enhanced.

The invention thus has an effect of realizing the inverter device andmotor-integrated type compressor having a small size and highreliability.

Because the inverter device has a small size, light weight, and highvibration resistance reliability, when applied in a vehicle airconditioner having a motor-driven compressor, the invention assures ahigh reliability of a control device including the inverter deviceagainst the vibrations peculiar to a vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an electric circuit diagram having an inverter deviceaccording to a first embodiment of the invention;

FIG. 2 is an explanatory diagram of a detecting method of an inducedvoltage in case of a sinusoidal driving in the above electric circuit;

FIG. 3 is a waveform diagram showing a voltage and current of asensorless DC brushless motor in the above inverter device;

FIG. 4 is a waveform diagram showing a modulation degree of each phaseat a maximum modulation degree 50% of two-phase modulation in the aboveinverter device;

FIG. 5 is a waveform diagram showing a modulation degree of each phaseat a maximum modulation degree 100% of two-phase modulation in the aboveinverter device;

FIG. 6 is a waveform diagram showing a modulation degree of each phaseat a maximum modulation degree 50% of three-phase modulation in theabove inverter device;

FIG. 7 is a waveform diagram showing a modulation degree of each phaseat a maximum modulation degree 100% of three-phase modulation in theabove inverter device;

FIG. 8 is a current feeding timing chart showing a phase currentdetecting method according to the first embodiment of the invention;

FIG. 9 is an electric circuit diagram showing a current route at acurrent feeding timing (a) of the above phase current detection;

FIG. 10 is an electric circuit diagram showing a current route at acurrent feeding timing (b) of the above phase current detection;

FIG. 11 is an electric circuit diagram showing a current route at acurrent feeding timing (c) of the above phase current detection;

FIG. 12 is an explanatory diagram showing a phase current detection oftwo-phase modulation according to the first embodiment of the invention;

FIG. 13 is an explanatory diagram showing a phase current detection ofthree-phase modulation according to the first embodiment of theinvention;

FIG. 14 is an explanatory diagram showing a phase current detection oftwo-phase modulation according to a second embodiment of the invention;

FIG. 15 is an explanatory diagram showing a phase current detection ofthree-phase modulation according to the second preferred embodiment ofthe invention;

FIG. 16 is an explanatory diagram showing a phase current detection ofthree-phase modulation according to a third embodiment of the invention;

FIG. 17 is a sectional view of a motor-driven compressor of an inverterdevice integrated type according to a fourth embodiment of theinvention;

FIG. 18 is a sectional view of a motor-driven compressor of an inverterdevice integrated type of another example of the invention;

FIG. 19 is a sectional view of a motor-driven compressor of an inverterdevice integrated type of still another example of the invention;

FIG. 20 is a system configuration diagram of an air conditioner for avehicle mounting a conventional motor-driven compressor;

FIG. 21 is a partially cut-away sectional view of a conventionalmotor-driven compressor;

FIG. 22 is a circuit block diagram of a conventional inverter devicecoupled assembly for 120-degree current feeding driving; and

FIG. 23 is a circuit block diagram of an inverter device coupledassembly for sinusoidal driving having a conventional current sensor forthe same phase current detection.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the invention are described below withreference to the accompanying drawings. It should be noted, however,that the invention is not limited to the illustrated preferredembodiments alone.

Embodiment 1

FIG. 1 is an electric circuit diagram of the present embodiment. In thediagram, reference numeral 1 is a battery, 2 is a switching element foran inverter operation connected to the battery 1, and 3 is a diode foran inverter operation. Reference numeral 4 is a stator winding of amotor, and 5 is a magnet rotor of the motor. Reference numeral 7 is acontrol circuit for controlling switching elements on the basis of asignal from a current sensor 6 acting as current detecting means.Reference numeral 37 is an inverter circuit, 20 is an inverter device,and 31 is the motor.

Here, comparing the electric circuit diagram in FIG. 1 with the electriccircuit diagram for 120-degree current feeding driving in FIG. 22, it isnot necessary to provide a comparator 128 and a phase shift circuit 127in the embodiment 1.

Further, comparing the electric circuit diagram in FIG. 1 with theelectric circuit diagram for sinusoidal driving having current sensorsfor phase current detection in FIG. 23, it is not necessary to provide acurrent sensor 130 for detection of U-phase current and a current sensor131 for detection of W-phase current in the embodiment 1.

A detected current value of the current sensor 6 is sent to the controlcircuit 7, and is used for calculating a power consumption and forprotecting the switching elements 2, and is further used for detecting aposition of the magnet rotor 5.

Hence, the control circuit 7 in the embodiment 1 does not require signalinput circuits (hardware) for the comparator 128 and phase shift circuit127 in FIG. 22 and for the current sensor 130 for detection of U-phasecurrent and the current sensor 131 for detection of W-phase current inFIG. 23, and it is enough to change a program software only.

Also, on the basis of a rotating speed command signal (not shown) andthe like, the switching elements 2 is controlled. As the current sensor6, a sensor using a Hall element or a shunt resistor can be used, andany will do so long as a peak value of the switching current from theswitching elements 2 can be detected.

Especially when using a shunt resistor, as compared with a sensor usinga Hall element, only the resistor is used, and there is no Hall elementthat requires attention to a vibration or the like, and hence a highreliability can be obtained. In contrast thereto, since the conventionalcurrent sensor 130 for detection of U-phase current and current sensor131 for detection of W-phase current in FIG. 23 are connected to outputportions of U phase or W phase where the potentials fluctuate, thereliability could not be enhanced by using a shunt resistor.

Moreover, since the current sensor 6 is designed to detect the peak ofthe switching current in order to protect the switching elements 2, itcan be used as it is.

In FIG. 1, the current sensor 6 is inserted to a minus side of a powersource line, but since the current is the same, it may be provided alsoat the plus side. By this arrangement, the number of components isdecreased as compared with the prior art, and the size and weight can bereduced, and the reliability such as a vibration resistance may beimproved at the same time. In particular, the vibration resistance isimportant since the current sensor and the like is mounted on a printedcircuit board, and in the configuration of the present embodiment, thevibration resistance is enhanced.

Referring now to FIG. 2, a method of detecting a position of the magnetrotor 5 is explained below.

FIG. 2 shows a relation between a phase current and an induced voltagein U phase. The induced voltage is a voltage induced in the statorwinding 4 due to the rotation of the magnet rotor 5 shown in FIG. 1, andhence it can be used for detecting the position of the magnet rotor 5.

The stator winding 4 in FIG. 1 includes a resistance R as well as aninductance L. The sum of the induced voltage, voltage of inductance Land voltage of resistance R is equal to the applied voltage from theinverter device 20. Supposing that the induced voltage is EU, phasecurrent is iU, and applied voltage is VU, the applied voltage VU isexpressed as: VU=EU+R·iU+L·diU/dt. FIG. 3 shows an example of one phaseof the voltage and current of the sensorless DC brushless motor.Accordingly, the induced voltage EU is expressed as:EU=VU−R·iU−L·diU/dt.

The control circuit 7 shown in FIG. 1 controls the switching element 2,and hence the applied voltage VU is known. Accordingly, by entering thevalues of the inductance L and resistance R in the program software ofthe control circuit 7, the induced voltage EU can be calculated bydetecting the phase current iU.

Next, the method of detecting the position of the magnet rotor 5 by thecurrent sensor 6 is explained.

First, waveforms of two-phase modulation and three-phase modulation areexplained. FIG. 4 shows a two-phase modulation at a maximum modulationdegree 50%, FIG. 5 shows a two-phase modulation at a maximum modulationdegree 100%, FIG. 6 shows a three-phase modulation at a maximummodulation degree 50%, and FIG. 7 shows a three-phase modulation at amaximum modulation degree 100%.

In the diagrams, reference numeral 41 is a U-phase terminal voltage, 42is a V-phase terminal voltage, 43 is a W-phase terminal voltage, and 29is a neutral point voltage. In the two-phase modulation, the graphextends in one direction from 0% to 100% along with increment of themodulation degree, while in the three-phase modulation, the graphextends in two direction from 50% toward 0% and 100% along withincrement of the modulation degree.

The operation is described below referring to a circuit diagram. FIG. 8shows an example of a current feeding of the upper arm switchingelements U, V, W and lower arm switching elements X, Y, Z within onecarrier (carrier period). In this case, in the two-phase modulation atthe maximum modulation degree 100% in FIG. 5, the phase of currentfeeding is about 80 degrees. There are three current feeding patterns(a), (b) and (c).

In the current feeding pattern (a), all of the upper arm switchingelements U, V, W are turned off, and all of the lower arm switchingelements X, Y, Z are turned on. FIG. 9 shows the current flow at thistime.

As clear from the diagram, the U-phase current and W-phase current flowfrom the diodes parallel to the lower arm switching elements X, Z to thestator windings 4, and the V-phase current flows from the stator winding4 to the lower arm switching element Y Hence, the current does not flowin the current sensor 6 and is not detected.

In the current feeding pattern (b), the upper arm switching element U isturned on and lower arm switching elements Y, Z are turned on. Thecurrent flow at this time is shown in FIG. 10.

As clear from the diagram, the U-phase current flows from the upper armswitching element U to the stator winding 4, the W-phase current flowsfrom the diode parallel to the lower arm switching element Z to thestator winding 4, and the V-phase current flows from the stator winding4 to the lower arm switching element Y Hence, the U-phase current flowsin the current sensor 6 and is detected.

In the current feeding pattern (c), the upper arm switching elements U,W are turned on, and the lower arm switching element Y is turned on. Thecurrent flow at this time is shown in FIG. 11.

As clear from the diagram, the U-phase current and W-phase current flowfrom the upper arm switching elements U and W to the stator windings 4,and the V-phase current flows from the stator winding 4 to the lower armswitching element Y Hence, the V-phase current flows in the currentsensor 6 and is detected.

Thus, since the U-phase current and V-phase current are detected, theremaining W-phase current is determined by applying the Kirchhoffcurrent law at the neutral point of the stator windings 4.

In this case, the U-phase current is a current flowing into the neutralpoint of the stator windings 4, and the V-phase current is a currentflowing out of the neutral point of the stator windings 4, and hence theW-phase current is determined by calculating the difference between theU-phase current and V-phase current.

Thus, the current can be detected in every carrier, and the position canbe detected in every carrier, so that the output to the stator windings4 can be adjusted. Accordingly, as compared with the 120-degree currentfeeding, torque fluctuations are made smaller, and a motor driving of alow noise and low vibration can be realized.

Especially in driving a motor mounted on a vehicle, a small size andlight weight, a high vibration resistance reliability, low vibration andlow noise are demanded, and such a control is preferable for controllinga drive of a motor-driven compressor and fan motors mounted on avehicle.

In the embodiment 1, it is known that the phase current to be detectedby the current sensor 6 is determined in the on/off state of the upperarm switching elements U, V, W. When only one phase is turned on, itsphase current is detected, when two phases are turned on, the current ofthe remaining phase is detected, and when all three phases are turned on(or turned off, no current can be detected. Therefore, by checking whichof the upper arm switching elements U, V, W in one carrier is turned on,the detectable phase current can be known.

In FIG. 12, the current to be detected is examined according to thisprinciple. In FIG. 12, the modulation degree in the phase range of −30degrees to 30 degrees in the two-phase modulation at the maximummodulation 100% is shown horizontally on the top, and the ON period ofthe upper arm switching elements U, V, W within one carrier (carrierperiod) at each phase corresponding to the above modulation degree isshown below by distributing and displaying uniformly from the center.

In the diagram, reference numeral 41 is the U-phase terminal voltage, 42is the V-phase terminal voltage, and 43 is the W-phase terminal voltage.In the lower part of the diagram, the current feeding period of the Wphase is indicated by a thick solid line, and the current feeding periodof U phase is indicated by a thin solid line. Arrows V and W shownbeneath each current feeding period indicate the current detectableperiod of the V phase and current detectable period of the W phase,respectively.

More specifically, at a phase −30 degrees, from the upper terminalvoltage diagram of each phase, the U-phase modulation degree is 0% andW-phase modulation degree is 87%, and the lower current feeding perioddiagram shows the modulation degree (current feeding time) of 87% of theW phase (thick lines) by distributing uniformly from the centersupposing that one carrier (carrier period) is 100%. The same as aboveare shown in the other phases.

Herein, the phase range is −30 degree to 30 degrees because this patternis repeated. The phase of the current to be detected is shown below theline. At the phase of −30 degrees and 30 degrees, it is known that thecurrent of only one phase can be detected. In this case, the previouslydetected value may be used again or other measure may be needed, butthere is a problem in the accuracy of detecting the position.

FIG. 13 shows a case in the phase range of 30 degrees to 90 degrees inthe three-phase modulation at the maximum modulation 100%, in which itis the same at 30 degrees and 90 degrees. The range is from 30 degree to90 degrees because this pattern is repeated. In the lower currentfeeding time period in FIG. 13, the V-phase current feeding period isindicated by a broken line, and an arrow marked U shows a U phasecurrent detectable period.

Embodiment 2

The embodiment 2 is explained with reference to FIG. 14 and FIG. 15. Theembodiment 2 is intended to enhance the accuracy of detecting theposition explained in FIG. 12 in the embodiment 1.

FIG. 14 shows the current feeding at the phase 30 degrees in FIG. 12, byshifting the U phase indicated by a thin solid line to the left side,and the W phase indicated by a thick solid line to the right side. As aresult, not only the V phase, but also the current of U phase andcurrent of W phase can be detected.

FIG. 15 shows the current feeding at the phase 30 degrees, by shiftingthe U phase to the left side, and the W phase to the right side in FIG.13. As a result, the current of U phase and current of W phase can bedetected. Also, in the current feeding at the phase 90 degrees, the Vphase is shifted to the left side and the W phase is shifted to theright side.

As a result, both currents of V phase and W phase can be detected. Atphases of 50 degrees and 70 degrees, by shifting the V phase largely tothe right side, the W phase can be also detected. Hence, in thethree-phase modulation, all of the three phases U, V, and W can bedetected by this method, and calculation of a current of the remainingphase after detecting two phases is not needed.

In the above explanation, the phases are specified, but it is evidentthat the same as above is obtained even if the phases are not specified.

According to this embodiment, the accuracy in detecting the position canbe more improved.

Embodiment 3

The embodiment 3 is explained with reference to FIG. 16. The presentembodiment in FIG. 16 shows another method of enhancing the accuracy indetecting the position explained in FIG. 12 in the embodiment 1.

First, an effect of a three-phase modulation is described.

For reducing vibrations, it is preferred to use a three-phasemodulation. In the three-phase modulation, the modulation range relativeto the phase range is narrower compared to the case of the two-phasemodulation, and a sinusoidal current is smoothed and a vibration becomessmaller.

In FIG. 8, in the case of the three-phase modulation, the ON period isadded also to the V phase. As a result, in the center of the carrierperiod, all three phases of U, V, and W are turned on. When the threephases are turned on, no current flows in the current sensor 6, and itis the same when all three phases are turned off (power is not suppliedto the motor from the power source in either case). Hence, the carrierperiod is divided into a former half and latter half, and electric poweris supplied (modulated). In other words, as compared with the two-phasemodulation, it is equivalent that the carrier period is half and thecarrier frequency is double.

Therefore, a fine and smooth sinusoidal current is supplied to themotor. Hence, in the three-phase modulation, as compared with thetwo-phase modulation, the noise and vibration can be further reduced.

In FIG. 6, for example, when 20% is added to each phase, the neutralpoint voltage (the sum of terminal voltages of phases being divided by3) is increased by 20%. Since the phase voltage is the difference valueof subtracting the neutral point voltage from the terminal voltage, theincrement of 20% is canceled, and the phase voltage is the same as thatbefore addition. It is the same in the case of a minus operation.

Hence, in the three-phase modulation, the phase voltage remains the sameeven if the same phase value is plus or minus in current feeding, and bymaking use of this nature, and in FIG. 16, the current feeding at thephase of 30 degrees in FIG. 13 is added to the left side in the U phaseand to the right side in the W phase. Equally to this plus portion, thecurrent feeding in the V phase is added. As a result, the current of Uphase and current of W phase can be also detected.

Also, by making use of this nature of the three-phase modulation thatthe phase voltage remains the same even if the same phase value is plusor minus in current feeding, the current feeding at the phase of 90degrees is subtracted to the left side in the V phase and to the rightside in the W phase. Equally to this minus portion, the current feedingin the U phase is subtracted at the right side. As a result, the currentof V phase and current of W phase can be also detected.

In the above explanation, the phases are specified, but it is evidentthat the same as above can be obtained even if the phases are notspecified. According to this embodiment, the position can be detectedmore accurately in the three-phase modulation.

Embodiment 4

FIG. 17 shows a coupled assembly of a motor-driven compressor with aninverter device coupled thereto according to the present embodiment 4.In FIG. 17, an inverter device 20 is installed closely contacting to theleft side of a motor-driven compressor 40, and a compression mechanism28, a motor 31 and others are installed in a metal casing 32. In thefollowing explanation, it is noted that the coupled assembly is alsocalled as “an inverter device integrated motor-driven compressor.”

A refrigerant is sucked in through a suction port 33, and is compressedas the compression mechanism 28 (a scroll in this example) is driven bythe motor 31.

The compressed refrigerant cools the motor 31 when passing through themotor 31, and is discharged from a discharge port 34. A terminal 39connected to the windings of the motor 31 inside is connected to theinverter device 20.

The inverter device 20 has a case 30 so as to be coupled to themotor-driven compressor 40. An inverter circuit 37 acting as a heatsource releases heat to a metal casing 32 of the motor-driven compressor40 by way of the case 30. That is, the inverter circuit 37 is cooled bythe refrigerant in the motor-driven compressor 40 by way of the metalcasing 32.

The terminal 39 is connected to an output of the inverter circuit 37.Connection wires 36 consist of power supply wires to the battery 1 andcontrol signal wires to the air conditioner controller. By using thewindings of the motor 31 of a concentrated winding, the length in thelateral direction can be made shorter as compared with that of adistributed winding. Since the inductance of the concentrated winding islarge, a reflux time to a diode is prolonged and the position detectionis difficult and therefore a control is difficult, but in a sinusoidaldriving, the position is detected by the current so that it is possibleto perform a control.

In such an inverter device integrated type motor-driven compressor, itis important that the inverter device 20 should be small in size and hasa strong vibration-proof, and it is preferable as the embodiment of thepresent invention.

FIG. 18 shows an example of the inverter device 20 which is installed atthe right side of the motor-driven compressor 40. The inverter circuit37 is cooled by a suction pipe 38. In order not to condense dew by thiscooling, the inverter device 20 is installed beneath the suction pipe38, so that the surrounding temperature of the inverter device 20 isalso lowered to decrease a temperature difference.

FIG. 19 shows an example of the inverter device 20 which is installedbetween the motor-driven compressor 40 and the suction pipe 38. In thiscase, the inverter circuit 37 is cooled by the suction pipe 38.

These two examples shown in FIG. 18 and FIG. 19 have the followingmerits.

That is, since the suction pipe 38 is not heated by the compressor 40,the efficiency of the compressor 40 is not lowered. The inverter device20 hardly condenses dew. Cool air from the suction pipe 38 flows down byconvection in the case 30, and the inside of the case 30 can be cooledefficiently. Besides, since the cool air flows down, the current sensor6 and controller 7 are also cooled (see FIG. 1) besides the invertercircuit 37, and the reliability of the inverter device 20 is assured.

The piping may be formed in any shape as desired such as flat. Aninsulating material or insulating space may be provided between theinverter circuit 37 or inverter device 20 and the compressor 40.

The motor 31 is preferably a sensorless DC brushless motor favorable forperforming a control in the embodiments 1 to 3. That is, the inverterdevice comprises an inverter circuit for switching the direct-currentvoltage from the direct-current power source by three-phase modulation,and supplying a sinusoidal alternating current to the sensorless DCbrushless motor having stator windings connected by three-phase wiringsand permanent magnet rotor, and one current detecting means fordetecting a current flowing through each of the stator windings of thesensorless DC brushless motor, and the inverter device judges theposition of the permanent magnet rotor by the current value detected bythe current detecting means so as to control the switching of theinverter circuit, whereby the current feeding timing to each phase ofthe stator windings of the sensorless DC brushless motor is shifted inthe carrier period to detect the current flowing in the stator windingby the current detecting means, so that the position of the permanentmagnet rotor is judged.

INDUSTRIAL APPLICABILITY

In the foregoing embodiments, the direct-current power source is abattery, but not limited to this, and the invention may be also appliedto the inverter device using a direct-current power source by rectifyingcommercial alternating-current power source, and driving an industrialmotor, or an inverter device (for such as a room air conditioner) fordriving a motor for electric household appliance, and others.

1. An inverter device for driving a sensorless DC brushless motor,comprising: an inverter circuit for switching a direct-current voltageobtained from a direct-current power source and supplying analternating-current current of a sinusoidal wave to the sensorless DCbrushless motor; and current detecting means for detecting a powersupply current between the direct-current power source and the invertercircuit, wherein the sensorless DC brushless motor includes statorwindings of a three-phase wiring (U, V, W) electrically connected to theinverter circuit and a magnet rotor, and the current detecting means isa single current detecting means which is used also for detecting thecurrent flowing in the stator windings, and by detecting the currentflowing in the stator windings as well as detecting the power supplycurrent, a rotational position of the magnet rotor is judged to therebycontrol the switching of the inverter circuit.
 2. The inverter deviceaccording to claim 1, wherein the direct-current voltage of thedirect-current power source is switched by three-phase modulation. 3.The inverter device according to claim 2, wherein within a carrierperiod of the three-phase modulation, a current feeding time is equallyadded or subtracted in a current feeding period in each phase of thestator windings.
 4. The inverter device according to claim 1, whereinwithin a carrier period, the current feeding timing to each phase of thestator windings is shifted, so that the current flowing in the statorwindings is detected by the current detecting means.
 5. The inverterdevice according to claim 1, which is adapted to be mounted on avehicle.
 6. The inverter device according to claim 1, driving thesensorless DC brushless motor which is a driving source of thecompressor.
 7. An air conditioner comprising a compressor, a sensorlessDC brushless motor acting as a driving source of the compressor, and aninverter device adapted for driving the brushless motor, wherein theinverter device comprises: an inverter circuit for switching adirect-current voltage obtained from a direct-current power source andsupplying an alternating-current current of a sinusoidal wave to thesensorless DC brushless motor; and current detecting means for detectinga power supply current between the direct-current power source and theinverter circuit, wherein the sensorless DC brushless motor includesstator windings of a three-phase wiring (U, V, W) electrically connectedto the inverter circuit and a magnet rotors, and the current detectingmeans is a single current detecting means which is used also fordetecting the current flowing in the stator windings, and by detectingthe current flowing in the stator windings as well as detecting thepower supply current, a rotational position of the magnet rotor isjudged to thereby control the switching of the inverter circuit.
 8. Theair conditioner according to claim 7, wherein the inverter deviceswitches the direct-current voltage from the direct-current power sourceby three-phase modulation.
 9. The air conditioner according to claim 8,wherein the inverter device, within a carrier period of the three-phasemodulation, a current feeding time is equally added or subtracted in acurrent feeding period in each phase of the stator windings.
 10. The airconditioner according to claim 7, wherein the inverter device shifts thecurrent feeding timing to each phase of the stator windings within acarrier period, so that the current flowing in the stator windings isdetected by the current detecting means.
 11. The air conditioneraccording to claim 7, wherein the inverter device is adapted to bemounted on a vehicle.
 12. The air conditioner according to claim 7,wherein the inverter device is integrally coupled to the compressortogether with the sensorless DC brushless motor.
 13. The air conditioneraccording to claim 12 comprising a suction pipe, which is adapted to thecompressor, for sucking a refrigerant for cooling the inverter device.14. The air conditioner according to claim 13, wherein the inverterdevice is disposed beneath the suction pipe.
 15. The air conditioneraccording to claim 13, wherein the inverter device is disposed betweenthe suction pipe and the compressor.
 16. The air conditioner accordingto claim 14, wherein the inverter device is disposed between the suctionpipe and the compressor.